How to lay lay retaining blocks to protect gas meter?

[fix]

There is a gas meter (and copper pipes) on side of the lawn, I have been thinking about ways to surround it with some sort of edging to protect it.

A concrete tree surround would have been convenient but it is too small: https://www.bunnings.com.au/custom-concrete-products-plain-edge-tree-surround_p3450013

Then I found these retaining blocks: https://www.bunnings.com.au/brighton-masonry-eziwall-lite-retaining-wall-block-charcoal_p0028944

7 pieces make required size (will turn the blocks around, so the locking edges are facing down):

Obvious step is to first clear the grass and make the half circle as flat and level as possible, given the small area and only one level of blocks, does it require sand and cement foundation? https://www.bunnings.com.au/australian-builders-20kg-sand-and-cement-mix-bag_p0760612

I plan to fill the area with pebbles or mulch, is a weed mat or some sort of plastic sheet necessary?

Thanks in advance for you input.

[MitchellMc]

Welcome to the Bunnings Workshop community @fix. It's amazing to have you join us, and many thanks for your question about laying retaining blocks.

That sounds like a good solution. However, I would recommend you consult with the gas supply company to ensure your addition isn't a safety concern. Say you made it two courses high; I would suggest that this then might be an issue as gas pools in low spots, and I can see this as breaking some regulations as it would be an explosion risk. I would suspect that you can't enclose a gas meter and even one course of blocks could be considered enclosing it. Best to check and be on the safe side.

There is no need to add a cement base, but that would certainly help hold them in position. I'd recommend you lay a 40mm bed of mortar and place the blocks onto it.

Adding a weed mat prior to your mulch or pebbles will assist in prevent unwanted weeds germinating and growing within the area.

Please let me know if you have any questions.

Mitchell